`let a = ref(None)` should not compile to `var a;` in a for loop

[aaronz0]

The following code:

   for i in 1 to 5 {
     let a = ref(None)
     if i == 3 {
       a := Some(3)
     }
     Js.log(a.contents)
   }

gets compiled to:

for(var i = 1; i <= 5; ++i){
  var a;
  if (i === 3) {
    a = 3;
  }
  console.log(a);
}

rescript playground

reason playground

Expected result:
Variable a is re-initialized to undefined in each iteration of the loop.

undefined
undefined
3
undefined
undefined

Actual result:

undefined
undefined
3
3
3

Correct compilation result should be:

for(var i = 1; i <= 5; ++i){
  var a = undefined;
  if (i === 3) {
    a = 3;
  }
  console.log(a);
}

[cristianoc]

I guess this will indirectly fix the issue?
#6102

[fhammerschmidt]

As a workaround you can use null from RescriptCore:

for i in 1 to 5 {
  let a = ref(null)
  if i == 3 {
    a := Value(3)
  }
  Js.log(a.contents)
}

[cknitt]

Fixed in v12 via #6102.